Out-of-Bounds Vulnerability in Linux Kernel CIFS Package
Summary
DEBIAN-CVE-2025-40099: In the Linux kernel, the following vulnerability has been resolved: cifs: parse_dfs_referrals: prevent oob on malformed input Malicious SMB server can send invalid reply to FSCTL_DFS_GET_REFERRALS - reply smaller than si... Affects linux versions 5.10.103-1 – 6.9.9-1. No fix is published. How to fix ↓
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Background
The Linux kernel is the core component of the Linux operating system, responsible for managing hardware and system resources. It provides essential services for all other software running on the system. The CIFS (Common Internet File System) module allows for file sharing over a network, enabling users to access files on remote servers. This vulnerability affects multiple Debian versions of the Linux kernel, making it critical for users relying on network file sharing functionalities.
Vulnerability Detail
In the Linux kernel, a vulnerability has been identified in the CIFS module related to the parsing of DFS referrals. A malicious SMB server can send an invalid reply to the FSCTL_DFS_GET_REFERRALS command, which may include a reply smaller than the expected size of the get_dfs_referral_rsp structure or a number of referrals that is less than specified in the header. This can lead to an out-of-bounds (oob) access, potentially allowing an attacker to exploit the system. The vulnerability is classified under CVE-2025-40099.
How To Fix
No fixed version is published for this vulnerability.
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Workaround
As a temporary workaround, users can limit exposure to this vulnerability by avoiding connections to untrusted SMB servers or by disabling the CIFS module if it is not required for their operations. This can be done with the command: 'sudo modprobe -r cifs'.
Conclusion
The CVE-2025-40099 vulnerability in the Linux kernel's CIFS module poses a significant risk to users of Debian systems. It is crucial to apply the necessary updates to mitigate this risk. Users are encouraged to monitor their systems for vulnerabilities using tools like Vulert and to follow best practices for security.
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FAQ
CVE-2025-40099 is a vulnerability in the Linux kernel's CIFS module that allows for out-of-bounds access due to improper handling of malformed DFS referral replies from SMB servers.
The vulnerability affects Debian versions 11, 12, 13, and 14 that utilize the Linux kernel.
You can use Vulert, which monitors open-source vulnerabilities in your software. By uploading your manifest file like package-lock.json, you can check for vulnerabilities without needing to install any software.
If exploited, this vulnerability could allow attackers to execute arbitrary code or crash the system, leading to potential data loss or unauthorized access.
Yes, you can temporarily disable the CIFS module or avoid connecting to untrusted SMB servers to mitigate the risk until an update can be applied.
References
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